Radiographic detector including block address pixel architecture, imaging apparatus and methods using the same

ABSTRACT

Embodiments of radiographic imaging systems; digital radiography detectors and methods for using the same can include radiographic imaging pixel unit cells that can include a plurality of N pixel elements that each include a photoelectric thin-film conversion element connected in-series to a conversion thin-film switching element, a conductor connected to the plurality of N pixel elements and an output switching element connected between the conductor and an imaging array output. Scan lines or row lines can extend in a first direction coupled to more than one pixel unit cell and data lines or column lines can extend in a second direction coupled to more than one pixel unit cell.

FIELD OF THE INVENTION

The invention relates generally to the field of medical imaging, and inparticular to radiographic imaging and digital radiographic (DR)detectors and more particularly to pixel structure or pixel layoutrelated to the use of non-single crystalline materials in sensors.

BACKGROUND

Stationary radiographic imaging equipment are employed in medicalfacilities (e.g., in a radiological department) to capture medical x-rayimages on x-ray detector. Mobile radiographic carts can include an x-raysource used to capture (e.g., digital) x-ray images on x-ray detector.Such medical x-ray images can be captured using various techniques suchas computed radiography (CR) and digital radiography (DR) inradiographic detectors.

A related art digital radiography (DR) imaging panel (e.g., flat paneldetector) acquires image data from a scintillating medium using an arrayof individual sensors, arranged in a row-by-column matrix, in which eachsensor provides a single pixel of image data. Each pixel generallyincludes a photosensor and a switching element that can be arranged in aplanar or a vertical manner, as is generally known in the art. In theseimaging devices, hydrogenated amorphous silicon (a-Si:H) is commonlyused to form the photodiode and the thin-film transistor switch neededfor each pixel. DR detectors can include several thousands of pictureelements, or pixels. In one known imaging arrangement, a frontplane hasan array of photosensitive elements, and a backplane has an array ofthin-film transistor (TFT) switches.

A traditional unit cell pixel architecture design used in digitalradiographic applications would contain 1 transistor element and 1photodiode element. A row of transistor elements would be controlled bya common row select control signal that can connect photodiode elementsto their respective output column (e.g., data line).

However, there is a need for improvements in the consistency and/orquality of medical x-ray images, particularly when obtained by an x-rayapparatus designed to operate with a-Si DR x-ray detectors.

SUMMARY OF THE INVENTION

An aspect of this application is to advance the art of medical digitalradiography.

Another aspect of this application to address in whole or in part, atleast the foregoing and other deficiencies in the related art.

It is another aspect of this application to provide in whole or in part,at least the advantages described herein.

An aspect of this application to is to provide methods and/or apparatusto address and/or reduce disadvantages caused by the use of portable(e.g., wireless) digital radiography (DR) detectors and/or radiographyimaging apparatus using the same.

An aspect of this application to is to provide radiographic imagingmethods and/or apparatus that can reduce a number of datalines for aradiographic imaging array.

An aspect of this application to is to provide radiographic imagingmethods and/or apparatus that can provide pixel unit cells that each caninclude N pixel output control units and N photosensor elements across Npixel columns to selectively connect to a single output dataline. In oneembodiment, the N pixel output control units across N pixel columns inthe pixel unit cell can be controlled by N additional, separate andindependent control signals.

An aspect of this application to is to provide radiographic imagingmethods and/or apparatus that can provide nit pixel architectureembodiments that can add one additional switching element across Ncolumns or rows. In one embodiment, the one additional switching elementcan selectively couple each of N photosensor elements in a pixel unitcell to a common dataline output, where N is a positive integer greaterthan 2.

An aspect of this application to is to provide radiographic imagingmethods and/or apparatus that reduce noise generated in a radiographicimaging array.

In accordance with one embodiment, the present invention can provide aradiographic imaging array, can include an insulating substrate; a scanline to extend in a first direction over the insulating substrate; adata line to extend in a second direction over the insulating substrate;and a thin film pixel unit cell including a first thin film switchingelement including a first terminal; a second terminal electricallycoupled to the data line; and a control terminal electrically coupled tothe scan line, wherein the first terminal and the second terminal areelectrically coupled based on a scan signal from the scan line; aplurality of N pixel elements each comprising a photoelectric thin filmconversion element and a second thin film switching element, where thephotoelectric thin film conversion element and the second thin filmswitching element are connected in-series between a first referencevoltage and a first terminal of the first switching element.

In accordance with one embodiment, the present invention can provide amethod of forming a digital radiographic detector including an indirectimaging pixel array, the method can include providing a scintillator foran indirect imaging pixel array; providing an insulating substrate forthe indirect imaging pixel array; providing scan lines extending in afirst direction; providing data lines extending in a second direction;and providing pixel unit cells, each pixel unit cell including a firstthin-film transistor element; a plurality of N pixel elements eachcomprising pairs of photoelectric thin film conversion element and asecond thin-film transistor where each pair of the photoelectric thinfilm conversion element and the second thin-film transistor areconnected in series between a first reference voltage and the firstswitching element, wherein the first thin-film transistor selectivelyconnects said each pair of the photoelectric conversion element and thesecond thin-film transistor to a single dataline within the pixel unitcell.

These objects are given only by way of illustrative example, and suchobjects may be exemplary of one or more embodiments of the invention.Other desirable objectives and advantages inherently achieved by thedisclosed invention may occur or become apparent to those skilled in theart. The invention is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of the embodiments of the invention, as illustrated in theaccompanying drawings.

The elements of the drawings are not necessarily to scale relative toeach other.

FIG. 1 is a diagram that shows a perspective view of a radiographicimaging apparatus including an area detector according to the presentapplication used for a radiographic procedure.

FIG. 2 is a diagram that shows schematic of a portion of an exemplaryimaging array for a radiographic detector according to the application.

FIG. 3A shows a perspective view of a portable wireless DR detector thatcan have utility in radiography imaging apparatus applications.

FIG. 3B is a diagram that shows a portion of a cross-sectional viewalong section line A-A of the portable wireless DR detector of FIG. 3A.

FIG. 4 is a diagram that shows an exemplary DR imaging array includingan embodiment of a unit pixel architecture for a DR detector accordingto the application.

FIG. 5 is a diagram that shows a pixel unit cell embodiment using Npixels and N+1 TFT elements according to the application.

FIG. 6 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIG. 7 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIG. 8 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIGS. 9A-9B are diagrams that show a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIG. 10 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIG. 11 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication.

FIGS. 12A-12B are diagrams that shows a portion of an exemplary DRimaging array including an embodiment of pixel unit cells according tothe application.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following is a description of exemplary embodiments of theinvention, reference being made to the drawings in which the samereference numerals identify the same elements of structure in each ofthe several figures.

Where they are used, the terms “first”, “second”, and so on, do notnecessarily denote any ordinal or priority relation, but may be used formore clearly distinguishing one element or time interval from another.

FIG. 1 is a diagram that shows a perspective view of an exemplary areadetector configured to include rows and columns of detector cells inposition to receive x-rays passing through a patient during aradiographic procedure. As shown in FIG. 1, an x-ray system 10 that canuse an area array 12 can include an x-ray tube 14 collimated to providean area x-ray beam 16 passing through an area 18 of a patient 20. Thebeam 16 can be attenuated along its many rays by the internal structureof the patient 20 to then be received by the detector array 12 that canextend generally over a prescribed area (e.g., a plane) perpendicular tothe central ray of the x-ray beam 16.

The array 12 can be divided into a plurality of individual cells 22 thatcan be arranged rectilinearly in columns and rows. As will be understoodto those of ordinary skill in the art, the orientation of the columnsand rows is arbitrary, however, for clarity of description it will beassumed that the rows extend horizontally and the columns extendvertically.

In exemplary operations, the rows of cells 22 can be scanned one (ormore) at a time by scanning circuit 28 so that exposure data from eachcell 22 can be read by read-out circuit 30. Each cell 22 canindependently measure an intensity of radiation received at its surfaceand thus the exposure data read-out can provide one pixel of informationin an image 24 to be displayed on a display 26 normally viewed by theuser. A bias circuit 32 can control a bias voltage to the cells 22.

Each of the bias circuit 32, the scanning circuit 28, and the read-outcircuit 30, can communicate with an acquisition control and imageprocessing circuit 34 that can coordinate operations of the circuits 30,28 and 32, for example, by use of an electronic processor (not shown).The acquisition control and image processing circuit 34, can alsocontrol the examination procedure, and the x-ray tube 14, turning it onand off and controlling the tube current and thus the fluence of x-raysin beam 16 and/or the tube voltage and hence the energy of the x-rays inbeam 16.

The acquisition control and image processing circuit 34 can provideimage data to the display 26, based on the exposure data provided byeach cell 22. Alternatively, acquisition control and image processingcircuit 34 can manipulate the image data, store raw or processed imagedata (e.g., at a local or remotely located memory) or export the imagedata.

Exemplary pixels 22 can include a photo-activated image sensing elementand a switching element for reading a signal from the image-sensingelement. Image sensing can be performed by direct detection, in whichcase the image-sensing element directly absorbs the X-rays and convertsthem into charge carriers. However, in most commercial digitalradiography systems, indirect detection are used, in which anintermediate scintillator element converts the X-rays to visible-lightphotons that can then be sensed by a light-sensitive image-sensingelement.

Examples of image sensing elements used in image sensing arrays 12include various types of photoelectric conversion devices (e.g.,photosensors) such as photodiodes (P-N or PIN diodes), photo-capacitors(MIS), or photoconductors. Examples of switching elements used forsignal read-out include MOS transistors, bipolar transistors, FETs, TFTsor switch components.

FIG. 2 is a diagram that shows a schematic of a portion of an exemplaryrelated art imaging array for a radiographic detector according to theapplication. As shown in FIG. 2, a schematic of a portion of anexemplary flat panel imager 240 can include an imaging array 212 havinga number of a-Si:H n-i-p photodiodes 270 and TFTs 271. An exemplary cell222 can include a photodiode 270 having its cathode connected to thesource (e.g., drain) of an FET 271. A bias circuit 232 can control abias voltage to the cells 222. Gate driver chips 228 can connect to theblocks of gate lines 283 and readout chips 234 (e.g., Read OutIntegrated Circuits (ROICs)) connect to blocks of data lines 284. Chargeamplifiers 286 can be provided that receive signals from the data lines284. An output from the charge amplifiers 286 can go to an analogmultiplexer 287 or directly to an analog-to-digital converter (ADC) 288to stream out the digital image data at desired rates.

In an exemplary hydrogenated amorphous silicon (a-Si:H) based indirectflat panel imager, incident X-ray photons are converted to opticalphotons, which are subsequently converted to electron-hole pairs withinthe a-Si:H n-i-p photodiodes 270. The pixel charge capacity of thephotodiodes is a product of the bias voltage and the photodiodecapacitance. In general, a reverse bias voltage is applied to the biaslines 285 to create an electric field (e.g., and hence a depletionregion) across the photodiodes and enhance charge collection efficiency.The image signal can be integrated by the photodiodes while theassociated TFTs 271 are held in a non-conducting (“off”) state, forexample, by maintaining the gate lines 283 at a negative voltage. Thearray 212 can be read out by sequentially switching rows of the TFTs 271to a conducting state using TFT gate control circuitry. When a row ofpixels is switched to a conducting (“on”) state, for example by applyinga positive voltage to the corresponding gate line 283, charge from thosepixels can be transferred along data lines 284 and integrated byexternal charge-sensitive amplifiers 286. After data is read out, therow can then be switched back to a non-conducting state, and the processis repeated for each row until the entire array has been read out. Thesignal outputs from the external charge-sensitive amplifiers 286 aretransferred to an analog-to-digital converter (ADC) 288 by aparallel-to-serial multiplexer 287, subsequently yielding a digitalimage. The flat panel imager having an imaging array 212 as describedwith reference to FIG. 2 is capable of both single-shot (e.g., static,radiographic) and continuous (e.g., fluoroscopic) image acquisition.

FIG. 3A shows a perspective view of a portable wireless DR detector 300according to embodiments of the application that can have utility inradiography imaging apparatus applications. FIG. 3B shows a portion of across-section view along line A-A of the DR detector 300. As shown inFIGS. 3A-3B, the portable DR detector 300 can enclose the imager 240including the imaging array 212.

In one embodiment, the DR detector 300 can include an enclosure 314including top panel cover 312 made of material that passes x-ray flux316 without significant attenuation. Scintillator 320 can be under(e.g., directly connected) the cover 312, the imaging array 212 can beunder the scintillator 320, and readout electronics can be co-planarwith the imaging array 212, partially below support member 324 or on aflexible connecter therebetween. The support member 324 can be includedto securely and/robustly mount the imager 240 and can further operate asa shock absorber between components therein and the enclosure 314. Thex-ray flux 316 can pass through the top panel cover 312, impinge uponscintillator 320 where stimulation by high-energy photons in the x-rayflux 316 can cause the scintillator 320 to emit low energy photons 332for detection by the imaging array 212. Device electronics required forproper operation of the detector 300 can be mounted within the enclosure314 and can include electronic components 328 (e.g., processors, FPGAs,ASICs, chips, etc.) that can be mounted on one or more separate and/orinterconnected circuit boards 326.

In the pixel architecture shown in FIG. 2, the number of datalines 284or column outputs is equal to the number of photodiodes 270 or pixelcolumns Therefore, the numbers of external ROIC input connections areequal to the number of pixel unit cell columns For example, in the caseof 1024 pixel columns, there are 1024 dataline external connectionsrequired. Exemplary commercially available external ROIC IC solutionscan handle 64 or 256 dataline inputs and therefore multiple ROICassemblies are used to satisfy a total of 1024 dataline output columns.For the above example, 16 64 ROIC IC assemblies or 4 256 ROIC ICassemblies can be used. Numerous ROIC IC assemblies can become asignificant portion of the overall radiographic detector cost and maynot be a feasible approach for lower cost radiographic applications.

Embodiments of a novel pixel architecture can include pixel unit cells,where each pixel unit cell can include N pixel output control units(e.g., N TFT elements or switches) and N photosensor elements across Npixel columns and 1 additional TFT that can then selectively connect asingle output dataline (e.g., shared) to the N TFT elements across Npixel columns Embodiments of a pixel unit cell can include N unit pixels(e.g., each unit pixel with a TFT element and a thin-film photosensorelement) and one additional pixel output control unit to selectivelycouple the N unit pixels of a pixel unit cell to a shared dataline.

Embodiments of novel pixel architectures and methods or apparatus forusing the same for digital radiographic applications are describedherein. Unit pixel architecture embodiments can add one additionalthin-film element (e.g., transistor) across N columns. According tocertain exemplary embodiments, the one additional thin-film transistor(TFT) can connect each of the N TFT elements associated with N thin-filmphotosensor elements to a common dataline column output where N is apositive integer greater than 2. The one additional TFT can becontrolled by a single common row select control signal. The N TFTelements across N pixel columns in the unit pixel architectureembodiments can be controlled by N additional, separate and independentcontrol signals (e.g., block address TFT elements). In exemplaryembodiments, to connect a photosensor to a dataline, a specificphotosensor (e.g., in N block address TFTs) and a specific row (e.g.,row select TFT) can be enabled together or concurrently. In certainexemplary embodiments, digital radiographic imaging detectors caninclude thin-film elements such as but not limited to thin-filmphotosensors and thin-film transistors. Thin film circuits can befabricated from deposited thin films on insulating substrates as knownto one skilled in the art of radiographic imaging. Exemplary thin filmcircuits can include amorphous-silicon devices such as a-Si PIN diodes,schottky diodes, MIS photocapacitors, and be implemented using amorphoussemiconductor materials, polycrystalline semiconductor materials such assilicon, or single-crystal silicon-on-glass (SiOG).

FIG. 4 is a diagram that shows an embodiment of a pixel unit cell for aDR detector according to the application. As shown in FIG. 4, pixel unitcell 410 can use one additional selector 420 across N photosensors 414respectively in N pixel elements 410 a, 410 b, . . . , 410 n in columns416. The selector 420 can electrically couple each of N TFT elements 412with a common dataline 430 output or column output. The selector 420 canbe controlled by a row select control signal 440 (ROW<1>, ROW<2>, . . ., ROW<m>). The N TFT 412 elements for N pixels 410 a, 410 b, . . . , 410n across N pixel columns 416 can be controlled by N separate andindependent control signals 450 (BA<1>, BA<2>, . . . , BA<N>) (e.g.,block address TFTs). The N TFT elements 412 selectively couple thephotosensors 414 to the selector 420 using a intra-pixel unit cellconnector 460. To connect a photodiode 414 in the pixel unit cell 410 toa dataline 430, a specific one of the TFTs 412 and selector 420 (e.g.,row select) can both be enabled together.

Embodiments according to the applications can provide variousadvantages. For example, the N TFT elements 412 in the pixel unit cell410 can reduce the number of datalines 430 in a DR imaging array 400 bythe number of independent control signals (e.g., a ratio of N). Forexample, in the case of 1024 pixel columns and N=8 separate unit pixelcontrol signals there can be 128 dataline external connections requiredcompared to 1024 for a related art pixel architecture. Reducing a numberof external dataline connections means that fewer ROIC IC assemblies canbe used. In the above example, 2 64 ROIC IC assemblies can be used incontrast to 16 64 ROIC IC assemblies or 4 256 ROIC IC assemblies usedfor 1024 pixel columns or datalines as shown in FIG. 2.

Another advantage to TFT elements 412 is that multiple unit pixelcontrol signals 450 can be enabled simultaneously to allow the charge ofmultiple photosensors or photodiode elements (e.g., horizontally) to betransferred to one dataline 430 output at one time (e.g., chargebinning). Concurrently reading multiple photosensor elements canincrease a signal to noise (SNR) ratio.

Further advantages to TFT elements 412 with independent control (e.g.,signals 450) is that subsampling of a pixel unit cell 410 for DR imagingarray 400 can be performed. Individual TFTs 412 may or may not beselected to allow for photodiode element charge subs ampling within thepixel unit cell 410. For example, not addressing or skipping blockaddress TFTs can represent horizontal sub-sampling of the pixel unitcell 410 or the DR imaging array 400.

An additional advantage is that charge binning and/or subsampling can bedone vertically in pixel unit cell 410 for the DR imaging array 400 byaccessing multiple rows 440. Given M rows 440, multiple row selectsignals can be accessed simultaneously for charge binning (e.g., addingtogether charge for photosensors in up to M rows), which can representvertical charge binning. Further, for M rows 440, specific rows within Mrows can be skipped or not accessed, which can represent verticalsubsampling. Further, horizontal charge binning and/or subsampling andvertical charge binning and/or subsampling can be performed concurrentlyusing the pixel unit cell 410.

FIG. 5 is a diagram that shows an embodiment of a pixel unit cell for aDR detector according to the application. As shown in FIG. 5, N pixelunit cells 410 can be repeatedly formed or laid out in pixel unit cell510 where N is the number of pixel block addresses contiguous orextending in one direction that can share a common output 505 forimproved fill factor. In one embodiment, the pixel unit cell 510 cancontain N+1 TFTs for selectable pixels. The common output 505 betweenthe TFTs can allow for a one output (e.g., dataline 430). As shown inFIG. 5, the pixel unit cell can connect unit pixels 410 a, 410 b, . . ., 410 n to node 505 using unit pixel connector 560.

For example, intra-pixel block sharing can reduce the overall datalinecapacitance compared to combining multiple vertical datalines togetheroutside the imaging data array. Further, reduced dataline capacitancecan reduce noise (e.g., thermal noise in the imaging array).

Embodiments of DR detector imaging arrays including independent pixeladdressing and methods for using the same can allow for combining and/orskipping photosensor elements in the horizontal direction within a pixelunit cell. Embodiments of a pixel unit cell (e.g., using an additionalTFT inside the pixel unit cell) can reduce or minimize an amount ofcolumn charge injection, which can be caused by multiplexing controlsignals. In an exemplary DR detector application, the dataline can beconnected to a ROIC that can put the dataline into at least two states,which can include a reset state and an integration state. In a firststate or the reset state, any charge collected or injected to thedataline that is connected to the ROIC can be removed. Thus, as amultiplexing switch can be located farther from the ROIC and closer to(e.g., within) the pixel unit cell, more dataline routing exists thatcan be reset by the ROIC. In the case of an end of column multiplexingarchitecture, a pixel array dataline side can be as long as the pixelarray and susceptible to any and/or all horizontal (e.g., row-based)and/or vertical (e.g., column based) control signals. In one embodimentaccording to the application, a pixel array dataline side can be smallor right at the pixel unit cell and can be only dependent on its' singlehorizontal (e.g., row-based) and/or vertical (e.g., column based)control signals. For example, increasing or maximizing the ROIC datalineside that can be placed in a reset state can reduce opportunities fornoise or injection charge.

Further, when a different number of switching events occurs because ofreadout configuration (e.g., subsampling or binning), differences in thenumber of feedthrough events can create readout specific configurationartifacts. Embodiments of a pixel architecture less susceptible toinjection charge outside of a pixel unit cell can reduce or avoidreadout configuration artifacts based on running different subsamplingand binning modes where pixels can be skipped or combined (e.g., vicefull readout modes).

From a radiographic imaging system or DR detector perspective, a readoutscheme can use, but is not limited to, an equal spatial subsamplingfrequency in the vertical direction just as in the horizontal direction.Embodiments according to the application can implement an imaging arrayarchitecture with equal (e.g., two) independently controlled row shiftregisters, for example, where one can control even rows and another cancontrol odd rows. FIG. 6 is a diagram that shows a portion of anexemplary DR imaging array including pixel unit cell embodiment 16pixels wide, which can use 17 TFT elements. As shown in FIG. 6, evenrows can contain pixel unit cells 610 in a given row that can becontrolled by a shift register 612 physically located on the left side(e.g., a first side) and odd rows can contains pixel unit cells 610′ ina given row that can be controlled by a shift register 614 physicallylocated on the right (e.g., a second side).

To readout all photosensors (e.g., photodiodes 414) in the array canrequire using the left shift 612 register row driver N times for allpixels in the even rows to readout N independently controlled blockaddress pixel elements in the even rows and then can require using theright shift register 614 row driver an additional N times for all pixelsin the odd rows to readout N independently controlled block addresspixel elements in the odd rows. Thus, up to a total of 2N sub-frames canbe used to readout all pixel elements as shown in FIG. 6.

FIG. 7 is a diagram that shows a portion of another exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication. Pixel unit cells 710 can be 8 pixels elements wide and canuse 9 switching elements. As shown in FIG. 7, a portion of an exemplaryDR imaging array can represent 4 rows and 8 columns and illustrate asub-frame readout sequence. As shown in FIG. 7, a left side register canread pixel unit cell 710 and a right side register can read pixel unitcell 710′ and 16 sub-frame readouts can be used to readout all pixelelements for an 8 wide pixel unit cell architecture.

FIG. 8 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication. Pixel unit cells 810 can be 8 pixels elements wide and canuse 9 switching elements. As shown in FIG. 8, a sub-samplingarchitecture (e.g., sub-sampling by 2) can reduce the number ofsub-frame readouts. As shown in FIG. 8, a lower resolution image wouldresult. In one example, the first 4 sub-frames 1, 2, 3, and 4 usingblock address control signals BA1, BA3, BA5, and BA7 are read using theleft shift register 612. Then, the second 4 sub-frames 5, 6, 7, and 8using block address control signals BA2, BA4, BA6, and BA8 can be readusing the right shift register 614. A total of N sub-frames can berequired for the sub-sample-by-2 implementation as shown in FIG. 8,where N is equal to 8. Exemplary grey regions 850 can represent unusedor not-required pixel elements. To achieve this particular horizontalpattern, N must be equal to or greater than 4 in a pixel unit cell. Asshown in FIG. 8, the imaging array architecture can allow for only onedataline 884 (e.g., vertical) to be present within the imaging array forany pixel unit cell horizontal pattern up to a pattern of Nphotosensors.

FIG. 9A is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication. Pixel unit cells 910 can be 8 pixels elements wide and canuse 9 switching elements. As shown in FIG. 9A, relative to the exemplaryby-2 subsampling approach over N sub-frames of FIG. 8, differentexposure gain settings can be implemented for each of the subframes(e.g., with existing ROIC architectures and ROIC timing configurations).Exemplary grey regions 950 can represent unused or not-required pixelelements. As shown in FIG. 9A, a dual exposure gain configuration for aby-2 subsampling can be implemented. Two gain settings G1 and G2 canresult in a 2 dimensional repeat pattern. A single dataline 930 can beused (e.g., vertical) for any pixel unit cell pattern up to a pattern ofN photosensors. Further, in an embodiment shown in FIG. 9B, up to 2Nexposure gain settings (e.g., independent and/or different) can be used.Gain can be changed along a row of an imaging array (e.g., betweensub-frames) that can be changed between sub-frame readouts.

FIG. 10 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication. Pixel unit cells 1010 can be 8 pixels elements wide and canuse 9 TFTs. As shown in FIG. 10, a by-4 charge binning configuration canbe implemented according to the application. Each 2×2 combinationrequires simultaneous clocking of the left and right shift register aswell as a pair of block address control signals (e.g., BA<1>, BA<2>, . .. , BA<8>) simultaneously. In this configuration it takes N/2 sub-framesto readout all pixel elements. A single dataline 1030 can be used (e.g.,vertical) for any pixel unit cell pattern up to a pattern of Nphotosensors.

FIG. 11 is a diagram that shows a portion of an exemplary DR imagingarray including an embodiment of pixel unit cells according to theapplication. Pixel unit cells 1110 can be 8 pixels elements wide and canuse 9 switching elements. As shown in FIG. 11, a combination of by-2charge summing and by-2 sub-sampling. The left shift register 612 can beused for 2 sub-frame readouts. A first subframe can use block addresssignals 1 and 2 together, and a second subframe can then use blockaddress control signals 5 and 6 together. The next 2 subframes readoutscan use the right shift register 614 where a first subframe can useblock address signals 3 and 4 together, and a second subframe can thenuse block address control signals 7 and 8 together. In the exemplaryconfiguration shown in FIG. 11, N/2 sub-frames can be used to readoutall required pixel elements.

Embodiments according to the application can implement (e.g., first)subframe flushing. After light exposure, a first frame can be readhaving no block address pixels on, which can be used to reset anyundesired charge as a function of light hitting switching elements.Embodiments using sub-frame flushing can also be used in subsampledmodes where the un-used or not-required pixels can also be included inthe first subframe flush. In embodiments using a two shift registerapproach, one first subframe flush can be used for the left shiftregister and one first frame flush can be used for the right shiftregister.

A disadvantage of the pixel design of FIG. 5A is an increase in chargetransfer time from the photodiode to the dataline as compared to theprior art pixel design of FIG. 2. The time constant for charge transferfrom the photodiode τ_(RC) is the product of the resistance of theTFT(s) R_(IFT) and the photodiode capacitance C_(PD). In the case wherethe block address TFT and the row select TFT are identical, the chargetransfer time constant for the block address architecture of FIG. 5A isdouble the charge transfer time constant for the single TFT pixel ofFIG. 2. This disadvantage may be overcome by a pixel design whichincludes a capacitor.

FIGS. 12A-12B are diagrams that shows a portion of an exemplary DRimaging array including an exemplary pixel unit cell embodiment. Asshown in FIGS. 12A-12B, additional capacitance can be added to a pixelunit cell to increase the readout rate when the imaging array isoperated in exemplary manners described herein. As shown in FIG. 12A, acapacitor 1292 with capacitance C_(CAP) can be added to a pixel unitcell 1210. A common voltage V_(CAP1) is applied the non-addressed plateof all capacitors in the imaging array. In order to reduce or minimizecharge transfer time, thereby increasing readout rate, C_(CAP) could bechosen to be less than the photodiode capacitance. Significantly reducedcharge transfer times may be achieved by choosing C_(CAP)<<C_(PD), suchas 25% or even 10% of C_(PD). As shown in FIG. 12B, a switched capacitorbank 1294 can be added to a pixel unit cell 1210′ where the capacitance(e.g., c1, c2, c3) can be selected based on characteristics such as theimaging modality or expected dosage.

Further, additional operating modes can operate using the pixel unitcell as shown in FIGS. 12A-12B. For example, a first operating mode cantransfer the change from the first block of photosensors/photodiodes tothe capacitors at the start of a block address (e.g., block 1 address).This operating mode comprises four steps: photodiode reset, exposure,block 1 charge transfer and block 1 readout; the block charge transferand block readout steps being repeated sequentially for each of theother blocks:

-   -   (a) Photodiode reset: The photodiode cathode is reset to a        voltage V_(CATHODE) by setting the gates of all row select        transistors into an “on” or conducting state, and the voltage on        gates of all block address transistors V_(BAG) to a voltage        V_(BAG)−V_(T)=V_(CATHODE) where V_(T) is the threshold voltage        of the block address transistors. In this mode, the detector is        prepared for start of exposure at any time an X-ray exposure is        requested by the radiographic technician.    -   (b) Charge integration and exposure: The imaging array is        exposed to light. The addressed plate of the capacitors in each        pixel are reset to a voltage V_(CAP2) by turning the gates of        all reset transistors into a conducting state and setting the        dataline voltage to V_(CAP2), where V_(CAP2)>V_(CATHODE). In        general, V_(CAP2) can be chosen such that        V_(CAP2)>V_(CATHODE)+qN_(MAX)/C, where N_(MAX) is the maximum        number of charge carriers anticipated during the exposure    -   (c) Transfer of block 1 photo-charge to capacitors: The charge        from the first block of photodiodes is transferred to the        capacitors by setting the block address transistors of block 1        to V_(BAG). Since V_(CAP2)>V_(CATHODE)+qN_(MAX)/C, all the        photo-charge will be transferred from the diode to the        capacitor,    -   (d) Readout of block 1 photo-charge: The dataline is set to        voltage V_(CAP2). The row select transistors are serially        addressed in order to transfer the charge from the capacitor to        the photodiode. The time constant of the charge transfer from        the capacitor to the photodiode is given by τ=R_(TFT)C_(CAP),        which is a reduction by 2× for the case where C_(CAP)=C_(PD), or        4× for C_(CAP)=C_(PD)/2, or 8× for C_(CAP)=C_(PD)/4. Of course,        the capacitor value C_(CAP) and the voltage V_(CAP2) should be        selected so as to ensure that the capacitor can hold the        selected or maximum expected photo-charge from the chosen        imaging modality: C_(CAP)*(V_(CAP2)−V_(CATHODE))>qN_(MAX).    -   The transfer step c and the readout step d is repeated for the        remaining blocks, after which the imaging array is ready for the        next exposure or for capture of dark reference frames for dark        offset correction.

The photodiode reset period (a) in the operating mode described abovemay be used for sensing the start of radiographic exposure. Since all ofthe block address gates and row select gates are in a conducting state,any photocharge incident upon any of the diodes is transferred onto therespective datalines. Sensing a change in current in the readoutcircuits would be indicative of a start of exposure. Sensing a change incurrent would trigger the transition from the reset state (a) to theexposure state (b). This would allow radiographic exposures to occurwithout timing synchronization between the X-ray generator and thedetector.

In an additional mode for sensing the start of exposure, the row selecttransistors may be maintained in an “off” state once the photodiodes andcapacitors have been reset in period (a). The current on the commonplate of the capacitor is sensed. At the start of exposure, thephoto-charge begins to accumulate on the addressed plate of thecapacitor; mirror charge flows from the power supply of the common plateonto the common plate of the capacitors. Sensing the start of currentflow could be used to trigger the transition from the exposure sensingto step (b)—charge integration.

The imaging mode described above applies to static radiographic imagingapplications, in which isolated single exposures are obtained. A secondoperating mode would apply to dynamic imaging applications, in which theradiographic exposure is continuous, such as fluoroscopy. In thisoperating mode the photodiode reset (a) and the exposure period (b) maybe eliminated. The photodiodes are continuously exposed and the chargereadout is also performed continuously, with the readout also serving toreset both photodiode and the capacitor.

It will be apparent to ones skilled in the art that alternativeoperating modes can be used with this architecture, For example, thecommon plate of the capacitor may be clocked either globally or on ablock-sequential mode rather than held at a DC potential to facilitatecharge storage and/or charge transfer.

In one embodiment, an imaging array for a DR detector can be configuredwith a single block rather than multiple blocks (e.g., the pixelarchitecture of FIG. 12A with a single block 1) where the block addressgate is a transfer gate, which can be used for dynamic imagingapplications.

Although embodiments of the application have been shown with a passivepixel architecture for the DR imaging array, various active pixelstructures can be used for the individual pixels in the pixel block orpixel unit cell described herein. Further, although embodiments of theapplication have been shown with a pixel architecture that can include asingle photosensor and a single TFT for the DR imaging array, variouspixel structures using 2 TFTs, 3 TFTs, 4 TFTs, 5 TFTs, 6 TFTs, 7 TFTs ormore TFTs with the single photosensor can be used for the pixel block orpixel unit cell described herein.

Embodiments of systems and/methods using pixel unit cells describedherein contemplate methods and program products on any computer readablemedia for accomplishing its operations. Certain exemplary embodimentsaccording can be implemented using an existing computer processor, or bya special purpose computer processor incorporated for this or anotherpurpose or by a hardwired system.

Exemplary embodiments herein can be applied to digital radiographicimaging panels that use an array of pixels comprising an X-ray absorbingphotoconductor, such as amorphous Selenium (a-Se), and a readoutcircuit. Since the X-rays are absorbed in the photoconductor, noseparate scintillating screen is required.

It should be noted that while the present description and examples areprimarily directed to radiographic medical imaging of a human or othersubject, embodiments of apparatus and methods of the present applicationcan also be applied to other radiographic imaging applications. Thisincludes applications such as non-destructive testing (NDT), for whichradiographic images may be obtained and provided with differentprocessing treatments in order to accentuate different features of theimaged subject.

Certain exemplary embodiments herein can be applied to digitalradiographic imaging arrays where photoelectric conversion elementsinclude at least one semiconductor layer, and that at least onesemiconducting layer can include amorphous silicon, micro-crystallinesilicon, poly-crystalline silicon, single-crystal silicon-on-glass(SiOG), organic semiconductor, and metal oxide semiconductors. Certainexemplary embodiments herein can be applied to digital radiographicimaging arrays where switching elements include at least onesemiconductor layer, and that at least one semiconducting layer caninclude amorphous silicon, micro-crystalline silicon, poly-crystallinesilicon, single-crystal silicon-on-glass (SiOG), organic semiconductor,and metal oxide semiconductors. Certain exemplary embodiments herein canbe applied to digital radiographic imaging arrays where the DR detectoris a flat panel detector, a curved detector or a detector including aflexible imaging substrate.

The array 212 can be divided into a plurality of individual cells 222that can be arranged rectilinearly in columns and rows. As will beunderstood to those of ordinary skill in the art, the orientation of thecolumns and rows is arbitrary, however, for clarity of description itwill be assumed that the rows extend horizontally and the columns extendvertically.

Consistent with exemplary embodiments, a computer program with storedinstructions that perform on image data accessed from an electronicmemory can be used. As can be appreciated by those skilled in the imageprocessing arts, a computer program implementing embodiments herein canbe utilized by a suitable, general-purpose computer system, such as apersonal computer or workstation. However, many other types of computersystems can be used to execute computer programs implementingembodiments, including networked processors. Computer program forperforming method embodiments or apparatus embodiments may be stored invarious known computer readable storage medium (e.g., disc, tape, \solid state electronic storage devices or any other physical device ormedium employed to store a computer program), which can be directly orindirectly connected to the image processor by way of the internet orother communication medium. Those skilled in the art will readilyrecognize that the equivalent of such a computer program product mayalso be constructed in hardware. Computer-accessible storage or memorycan be volatile, non-volatile, or a hybrid combination of volatile andnon-volatile types.

It will be understood that computer program products implementingembodiments of this application may make use of various imagemanipulation algorithms and processes that are well known. It will befurther understood that computer program products implementingembodiments of this application may embody algorithms and processes notspecifically shown or described herein that are useful forimplementation. Such algorithms and processes may include conventionalutilities that are within the ordinary skill of the image processingarts. Additional aspects of such algorithms and systems, and hardwareand/or software for producing and otherwise processing the images orco-operating with computer program product implementing embodiments ofthis application, are not specifically shown or described herein and maybe selected from such algorithms, systems, hardware, components andelements known in the art.

While the invention has been illustrated with respect to one or moreimplementations, alterations and/or modifications can be made to theillustrated examples without departing from the spirit and scope of theappended claims. In addition, while a particular feature of theinvention can have been disclosed with respect to only one of severalimplementations/embodiments, such feature can be combined with one ormore other features of the other implementations/embodiments as can bedesired and advantageous for any given or particular function. The term“at least one of” is used to mean one or more of the listed items can beselected. The term “about” indicates that the value listed can besomewhat altered, as long as the alteration does not result innonconformance of the process or structure to the illustratedembodiment. Finally, “exemplary” indicates the description is used as anexample, rather than implying that it is an ideal. Other embodiments ofthe invention will be apparent to those skilled in the art fromconsideration of the specification and practice of the inventiondisclosed herein. It is intended that the specification and examples beconsidered as exemplary only. The scope of the invention is indicated bythe appended claims, and all changes that come within the meaning andrange of equivalents thereof are intended to be embraced therein.

What is claimed is:
 1. A projection radiographic imaging array,comprising: an insulating substrate; a scan line to extend in a firstdirection over the insulating substrate; a data line to extend in asecond direction over the insulating substrate; and a thin film pixelunit cell comprising a first thin film switching element comprising: afirst terminal; a second terminal electrically coupled to the data line;and a control terminal electrically coupled to the scan line, where thefirst terminal and the second terminal are electrically coupled based ona scan signal from the scan line; a plurality of N pixel elements eachcomprising a photoelectric thin film conversion element and a secondthin film switching element, where the photoelectric conversion elementand the second switching element are connected in series between a firstreference voltage and a first terminal of the first switching element.2. The radiographic imaging array of claim 1, where the photoelectricconversion element is a photosensor, and the pixel unit cell comprisesan N-photosensor pixel block and N+1 switching elements.
 3. Theradiographic imaging array of claim 1, comprising a plurality of N blockaddress lines that respectively connect to a control terminal of one ofthe plurality of N second switching elements.
 4. The radiographicimaging array of claim 1, where a selected second switching element andthe first switching element are both enabled to connect onephotoelectric conversion element to a corresponding data line.
 5. Theradiographic imaging array of claim 1, where a number of data linesconnections in the radiographic imaging array is less than a number ofphotoelectric conversion elements in a row extending in the firstdirection, where the number of data lines in the imaging array isreduced by a ratio of 1/N.
 6. The radiographic imaging array of claim 1,comprising a plurality of N block address lines each electricallycoupled to select one of the N second switching elements, where multipleblock address control signals simultaneously enabled transfer a chargeof multiple photoelectric conversion elements in the pixel unit cell toone data line for output at one time.
 7. The radiographic imaging arrayof claim 6, where charge binning of pixel elements positions along thefirst direction is configured to increase a signal to noise (SNR) valueof data output by the radiographic imaging array.
 8. The radiographicimaging array of claim 6, comprising a plurality of N block addresslines each electrically coupled to select one of the N second switchingelements, where at least one block address control signal is notselected when outputting charge from the plurality of photoelectricconversion elements to sub-sample charge among the plurality ofphotoelectric conversion elements in the pixel unit cell, whereaddressing less than all of the second switching elements or skippingsecond switching elements in the pixel unit cell provides horizontalsub-sampling of the radiographic imaging array.
 9. The radiographicimaging array of claim 1, comprising a plurality of N block addresslines each electrically coupled to select one of the N second switchingelements, where multiple block address control signals simultaneouslyenabled transfer a charge of multiple photoelectric conversion elementsin the pixel unit cell to one data line for output at one time, wherethe first frame is read having no block address control signals enabledto reset the photoelectric conversion elements in the pixel unit cell,where the first frame is configured to use a subset of the multipleblock address control signals to reset a corresponding subset of thephotoelectric conversion elements in the pixel unit cell.
 10. Theradiographic imaging array of claim 1, comprising a plurality of N blockaddress lines each electrically coupled to select one of the N secondswitching elements, where vertical photoelectric conversion elementcharge binning is performed by accessing multiple second switchingelement rows, where for M scan lines, multiple scan line select signalscan be accessed simultaneously with multiple block address lines forvertical charge binning of the imaging array.
 11. The radiographicimaging array of claim 1, where non-adjacent photoelectric conversionelements have their corresponding charge binned using the firstswitching element, a single data line and multiple block addresssignals.
 12. The radiographic imaging array of claim 1, firstphotoelectric conversion elements from a plurality of pixel unit cellshave their corresponding charge binned using multiple scan lines andmultiple block address signals.
 13. The radiographic imaging array ofclaim 1, comprising: a first shift register coupled to a first subset ofscan lines; and a second shift register coupled to a second differentsubset of scan lines.
 14. The radiographic imaging array of claim 13,where the first shift register and the second shift register areimplemented in thin-film transistors on the imaging array.
 15. Theradiographic imaging array of claim 1, where a number of pixel unitcells is greater than three, greater than four or greater than five inthe first direction or the second direction.
 16. The radiographicimaging array of claim 1, where the second thin film switching elementcomprises: a first terminal; a second terminal electrically coupled tothe first terminal of the switching element, and a control terminalelectrically coupled to an independent block address line, where thefirst terminal and the second terminal of the second switching elementare electrically coupled based on a signal at the independent blockaddress line; and where the photoelectric conversion element, comprises,a first terminal electrically coupled to the first reference voltage,and a second terminal electrically coupled to the first terminal of thesecond switching element; and further comprising a reference voltageline to connect to the first reference voltage to the first terminal ofa plurality of photoelectric conversion elements.
 17. The radiographicimaging array of claim 1, further comprising a digital radiographicimaging apparatus comprising a x-ray source, an x-ray detector andcontrol parameters input device, where the x-ray detector is portableand wireless or tethered, where the x-ray detector comprises a flatpanel radiographic detector, a DR detector, a curved DR detector, or aflexible substrate.
 18. The radiographic imaging array of claim 1, wherethe photoelectric conversion element includes at least one semiconductorlayer, and that at least one semiconducting layer is selected from thegroup of amorphous silicon, micro crystalline silicon, poly-crystallinesilicon, single-crystal silicon-on-glass (SiOG), organic semiconductor,and metal oxide semiconductors, where the switching element includes atleast one semiconductor layer, and that at least one semiconductinglayer is selected from the group of amorphous silicon, micro crystallinesilicon, poly-crystalline silicon, single-crystal silicon-on-glass(SiOG), organic semiconductor, and metal oxide semiconductors.
 19. Theradiographic imaging array of claim 1, further comprising: at least oneimaging array comprising: a plurality of pixel unit cells arranged inrows and columns, where the scan line and the data line are common tomore than one pixel unit cell, driving circuits coupled to a pluralityof rows of the imaging array, readout circuits coupled to a plurality ofcolumns of the imaging array; and a conversion screen configured toconvert first radiation of one or multiple wavelength range into seconddifferent radiation of one or multiple wavelength range proximate to theplurality of pixel unit cells.
 20. A method of forming a digitalradiographic detector including an indirect imaging pixel array, themethod comprising: providing a scintillator for an indirect imagingpixel array; providing an insulating substrate for the indirect imagingpixel array; providing scan lines extending in a first direction;providing data lines extending in a second direction; and providingpixel unit cells, each pixel unit cell comprising a first thin-filmtransistor element; a plurality of N pixel elements each comprisingpairs of photoelectric thin-film conversion element and a secondthin-film transistor where each pair of the photoelectric thin-filmconversion element and the second thin-film transistor are connectedin-series between a first reference voltage and the first switchingelement, where the first thin-film transistor selectively connects saideach pair of the photoelectric conversion element and the secondthin-film transistor to a single dataline within the pixel unit cell.